The invention relates to a contact device with at least a first contact region, which is designed for electrical connection to an electric line, and at least a second contact region, which is designed for electrical connection to a flexible circuit board or some other contact medium which becomes damaged as a result of repeated soldering, the first contact region and the second contact region being connected electrically. The invention also relates to a method of producing an electrical connection between an electric line and a flexible circuit board.
Electrical connections between and within complex subassemblies are increasingly being realized using flexible circuit boards, also referred to as flexible foils. In comparison with electrical cable connections, these have a series of advantages. A flexible circuit board allows good movement of components of the subassemblies in relation to one another, in particular also during fitting. Furthermore, in comparison with conventional cables, a flexible circuit board takes up less space and, at the same time, can be subjected to relatively high mechanical loading. A flexible circuit board is used to connect, for example, various electronic components, such as sensors, actuators, etc., electrically to a control electronics unit. The transition between conventional cable technology and a flexible circuit board takes place, according to the prior art, by a flex or a contact pin being soldered directly onto the flexible circuit board. This method of contact connection has the disadvantage that, in the event of the component which is contact-connected in this way to the flexible circuit board being exchanged, the flexible circuit board may be damaged by soldering heat. It is thus usually only possible for this soldering operation to be easily carried out once, which is disadvantageous in particular in the case of repair or exchange.
The object of the invention is to provide a device and a method which are intended for the contact connection of an electric line and a flexible circuit board or some other contact medium which becomes damaged as a result of repeated soldering, and avoid the abovementioned problems and, in particular in the case of the connection between the device and the electric line being broken and reinstated, avoid damage to the flexible circuit board.
This object is achieved by the features of the independent claims.
Advantageous embodiments of the invention are given in the dependent claims.
The invention builds on the contact device of the generic type by providing, between the first contact region and the second contact region, a third region which has a thermal conductivity per unit length which is lower than the thermal conductivity per unit length of the first contact region and/or the thermal conductivity per unit length of the second contact region. The envisaged third region with a lower thermal conductivity per unit length hinders or slows down the transfer of heat, where a large amount of heat has been supplied at the first contact region, to the second contact region, which is thermally connected to the thermally more sensitive flexible circuit board. In this way, the connection between the first contact region and an electric line can be produced and broken as often as desired even when this operation is associated with a significant temperature rise in the first contact region. In contrast to the prior art, in which there is no provision made to prevent the transfer of heat, or to make it more difficult, the present invention considers, in particular, heat transmission from the one contact region to the other contact region and makes this more difficult using suitable measures. This heat transmission determines a preferred direction, to which the thermal conductivity per unit length is to be referred in particular. The expression thermal conductivity per unit length here is intended to cover those properties of the respective region on which a transfer of the heat between the contact regions depends, for example the spatial configuration, material parameters, etc. Moreover, as a result of the transfer of heat which is applied at the first contact region being made more difficult or slowed down, heat-loss mechanisms such as radiation or convection have a greater effect, and the adverse effect on the second contact region is thus additionally reduced.
In the case of a preferred embodiment, it is provided that the lower thermal conductivity per unit length of the third region is brought about in that the third region has an effective cross section in the heat-transfer direction which is smaller than the effective cross section of the first contact region in the heat-transfer direction and/or the effective cross section of the second contact region in the heat-transfer direction. This constitutes an embodiment which is relatively straightforward to realize in production terms. It is possible here, for example, for the geometrical cross section of the third region to be achieved by a reduction in the circumference, that is to say, for example, by the formation of a tapered portion, of a constriction or the like. As an alternative, it is also possible to reduce the cross section by segmentation in the heat-flow direction, that is to say, for example, by the formation of a plurality of heat-transmission regions with a particularly small cross section, which may be expedient, in particular, from mechanical standpoints.
As an alternative, or in addition, it may be provided, in the case of an advantageous embodiment, that the lower thermal conductivity per unit length of the third region is brought about in that the material of the third region has a lower thermal conductivity per unit length than the materials of the first contact region and/or the second contact region. This embodiment, by providing at least two different materials, means that more stringent requirements have to be met by production, but, if the materials are suitably selected, it can bring about particularly good thermal isolation of the two contact regions.
In the case of a likewise advantageous embodiment, it is provided that the task of connecting the first contact region electrically to the electric line and/or the task of connecting the second contact region electrically to the flexible circuit board comprises at least one soldering operation. The operation of soldering at least one of the two electrical connections of the contact device constitutes a particularly straightforward, cost-effective and reliable connection method.
In particular in the case of an advantageous embodiment, it may be provided that the main directions in which the first contact region and the second contact region are positioned enclose an angle of essentially 90°. Such an arrangement makes it easier, for example, to produce the electrical connection between the electric line and the contact device.
In the case of an advantageous embodiment, it may be provided the first contact region has a contact surface suitable for soldering purposes. This aids the production of the electrical connection between the first contact region and that electric line.
Furthermore, it may advantageously be provided that the contact surface at least partially accommodates the electric line. The soldering operation may thus be facilitated to the extent where the electric line which is to be fitted is introduced into the contact surface prior to the soldering operation and retained there during the soldering operation.
It may also be provided, in the case of a preferred embodiment, that the second contact region is of essentially cuboidal or cylindrical design. This constitutes an easy-to-produce basic shape which is suitable for contact connection to a flexible foil.
It is further advantageous if the contact device has a latching and/or a plug-in portion. This allows straightforward fastening of the contact device, for example, on a carrier which retains the flexible circuit board.
It may likewise preferably be provided that the latching and/or plug-in portion, the first contact region, the second contact region and the third region are connected by a common basic body. It may be advantageous here, in certain circumstances, for the basic body to be of significantly greater dimensions than the third region, and possibly also than the second contact region, in order to achieve sufficient mechanical stability for the device as a whole.
The invention also relates to a method of producing an electrical connection between an electric line and a flexible circuit board, comprising the following steps:                providing a rigid contact device, in particular a contact device according to the invention,        connecting a first contact region of the rigid contact device to an electric line, and        connecting a second contact region of the rigid contact device to a flexible circuit board.        
In the case of a preferred embodiment of the method, it may be provided that the connection comprises at least one soldering operation.
In this way, the advantages of the invention are also realized within the context of a method.
The invention is based on the finding that the cable flex or the pin of an electromechanical component is contact-connected not directly to the flexible foil, but to the one end of a conductive transfer location, of which the other end is contact-connected to the flexible foil. In the case of exchange being necessary, the cable flex or the pin can be detached and attached a number of times, by soldering, without the flexible foil being subjected to loading, or becoming damaged, in the process.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.